Burner control system



3,079,932 Patented Mar. 5, 1963 free 3 M9332. BURNER coisrnoi. SYSTEM Eernardus J. taring, Markham, @ntario, Canada, assignor, by mesne assignments, to White-Rodgers Company, a corporation of Missouri Filed Dec. 14, 196i, ar. No. 159,295 Claims. (Ci. 158--28) This invention relates to automatic control systems for fluid fuel burners which include safety means operative to permit the continued supply of fuel to the burner when there is combustion and to cut off the flow of fuel if cornbustion fails to occur within a predetermined interval during which fuel is supplied or if combustion having been established subsequently fails.

An object of the invention is to provide a generally new and'irnproved safety control system for fluid fuel burners incorporating an instantly responsive flame detection means which is particularly economical in construction and reliable in operation.

A further object is to provide a burner control system employing a semiconductor-type, light-sensitive element as a combustion flame detector in such a manner as to require only slight current flow through the element in per formance of its function.

A further object is to provide a burner control system employing a semiconductor-type, light-sensitive element as a combustion flame detector in such manner that operation of the fuel supply means cannot be initiated if the light sensitive element is improperly installed so as to be affected by light other than the light of combustion or if the element is or becomes defective in a manner as to be operatively conductive in the absence of light.

A further object is to provide a burner control circuit having a voltage dependent resistor and a semiconductortype, light-sensitive element in parallel connection, wherein a predetermined voltage commonly applied through a fixed resistance effects a functional conductance of the voltage dependent resistor whenlight energy impinging the parallel connected, light sensitive element is less than that which occurs when there is burner flame and wherein conductance of the light sensitive element when impinged by the light of burner flame or its equivalent is sufficient to result in a drop to non-functional conductance of the parallel connected, voltage dependent resistor.

Further objects and advantages will appear from the following description when read in connection with the accompanying drawing.

FIG. 1 of the drawing is a diagrammatic illustration of a control system for a conventional, pressure type, oil burner embodying a form of the present invention; and

FIG. 2 is a portion of a characteristic voltage/current curve of the voltage dependent resistor.

FIG. 3 is a partially sectionalized view of a conventional pressure-type oil burner showing the mounting position of the light sensitive element.

Referring to the drawing, the primary elements of the system are: an oil burner 10 having a driving motor 12, a space thermostat 14 responsive to the temperature of a space being heated by the burner, an ignition relay having a winding 16 and contacts 13, a motor relay having a winding 29, motor contacts 22, and holding contacts 24-, a flame detector relay having a winding 26 and contacts 28,

a thermal safety time switch havin contacts 3%} and a and a secondary winding '58, and power supply leads 60 and 62 for connection to a suitable A.C. power source.

The oil burner it) includes the usual blower and fuel pump which when driven by the motor 12 supplies ato-. ized oil and combustion air to the burner nozzle where it is ignited by spark at electrodes 52. The motor 12 is energized through a circuit traced from power supply lead 60 through a lead 64, motor relay contacts 22, a lead 66, motor 12, and a lead 68 to power lead 62. The igniter is energized through a circuit extending from the lead 64 through a lead 7t), ignition relay contacts 18, a lead 72, the primary winding of ignition transformer 54, and a lead 74- to the lead 68.

The ignition relay winding 16 is energized through a low voltage circuit extending from one side of transformer secondary 53 through a lead 76, safety switch contacts 30, a lead 78, a lead 80, a lead 82, safety switch heater 32, a lead 3'4, cold side contact 34 of the scavenger switch, the switch blade 38, a lead 36, a lead 88, relay winding 16, a lead ti, a lead 92, a lead 94, a lead 96, through thermostat 14 and a lead 98 to the other side of secondary Winding 58.

The motor relay winding 29 is energized initially through a low voltage circuit starting at the right side of secondary Winding 58 through lead 76, safety switch contacts 3%, lead 78, lead 80, lead 82, safety switch heater 32, lead 34, cold side contact 34 and blade 38, lead 86, a lead roe, flame detector relay contacts 28, a lead 102, relay winding 2ft, lead 92, lead 94, lead 96, through thermostat l4, and lead 98 to the other side of transformer secondary 58.

When the motor relay pulls in, energization of its winding Ed is maintained by a branch circuit extending through its holding contacts 24. This branch circuit parallels the safety switch heater 32 and the flame detector relay contacts 23, and extends from the g'unction of leads 3d and through lead 8%, through holding contacts 24-, lead lild, scavenging switch heater 4d, a lead res, and through lead to one side of the motor relay wind- The flame detector relay winding 26 is energized through a circuit which may be traced from thermostat to through the lead 96, current limiting resistor 42, a lead res, voltage dependent resistor 44, a lead 110, the winding 26, a lead 112, rectifier 36, a lead 114, lead '75, safety time switch contacts 3%, lead 7s, transformer secondary 5S, and lead 8 to the thermostat. A capacitor 48 is connected across the flame detector relay winding to the leads lit and 112 to prevent relay hum. The semiconductor, light sensitive element St) is connected between leads liid and lid and is therefore in parallel with the voltage dependent resistor 44 as well as with the fiame detector relay winding and the rectifier. It is to be noted that the current passing through element St) is, therefore, alternating and not rectified as it is in the network of the relay winding 26.

The safety time switch 39 is normally closed, but when its bimetal blade is heated for a predetermined period of time by resistance heater 32 when fully energized, it warps open and locks in an open position requiring resetting. This type of safety switch is commonly used and its construction and operation are well understood in the art.

The voltage dependent resistor id is a commercially available element developed and used primarily for voltage regulation and stabilization. its structure consists of a eonglomeration of silicon carbide crystals in a ceramic binder pressed into a desired shape and then sintered. The voltage dependency of the element is apparently due to contact resistance between carbide crystals. The characteristic voltage/current curve of the element is nonlinear, and while at higher voltages the curve straightens very rapidly with slight voltage increase.

The characteristics of the particular element 44 are such that it has ample conductancein the circuit at the voltage applied to energize relay winding 26 and close the contacts 23 when the resistance of parallel connected,

' light sensitive cell Silis sufficiently high, but when slight conduction occurs through parallel connected element 50 due to light energy of combustion impinging thereon,

conduction through element 44.drops sharply due to the voltage drop across resistor 42v and relay contacts 23 en. i

The light sensitive element 50 is of the semiconductor type Which in the absence of the light of burner flame has extremely high electrical resistance, but becomes sufciently conductive when exposed to the light of burner flame to effect a considerable reduction in conduction through the parallel voltage dependent resistor element 44. Light sensitive element 50 is preferably mounted within the burner casing at the rear end of the blast tube, as indicated in FIG. 3. It has been found that ample light energy reaches the element in this position, either directly or by reflection, to effect its operational conductance while, on the other hand, in the absence of burner flame, it is sufiiciently shielded from ambient li ht.

The current limiting resistor '42 has such value as to limit the total current through the parallel connected, voltage dependent resistor and light sensitive element to a range wherein the described interaction between light sensitive element 50 and voltage dependent resistor 44 will occur. The flame detector relay is preferably a highly sensitive, encapsulated, reed-type relay, the rectifier 46 is preferably a semiconductor diode, and the capacitor 48 is preferably of the electrolytic type.

Operation 20 effects the closing of its motor contacts 22, thereby energizing burner motor 12 to supply fuel and air for combustion which is ignited by igniter 52. .The ener gization of motor relay winding 20 also effects the closing of its holding contacts- 24,- which completes the described branch circuit for the winding which includes the scavenging switch heater 40, but bypasses the safety switch heater 32, and flame detector contacts 28.

Under these conditions, when motor relay holding contacts 24 close, the'safety switch heater 32 remains connected in series with the ignition relay winding 16 through the cold contact side 34 of the scavenging switch and the scavenging switch heater 4% is now connected in series with the motor relay; but these two pairs of series connected elements are also electrically interconnected through the closed flame detector relay contacts 28 and the lead 100 which places the impedance of the ignition winding in parallel with the motor relay winding with respect to safety switch heater 32. The impedance of ignition relay winding 16 is considerably greater than that of the motor relay winding so that the effect of breaking this interconnection bythe opening of flame detector relay contacts 28 is to place safety switch heater 32 in series with the higher impedance ignition relay Winding only, which considerably reduces the heat output of the, heater 32. It is to be noted that while the scavenger switch heater 4t is placed in series with. the motor relay winding 2%? when holding contacts 24 close, the pull-in circuit for the motor relay winding 20 extends, nevertheless, through the safety switch heater 32 alone, so that the motor relay winding 2% cannot be initially energized except through the safety switch heater.

When combustion at the burner occurs light sensitive element 59 becomes sufficiently conductive to result in a voltage drop across resistor 42 which effects such decrease in the voltage applied to voltage dependent resistor 44 as to render it insutliciently conductive to maintain operative energization of flame detector relay winding 26 and therefore flame detector relay contacts 23 open. When this occurs the safety switch heater32 is placed in series with the higher impedance, ignition relay winding 16 only, and its heat output is, therefore, substantiallyreduced so that safety switch bimetal blade 30 is now heated at a considerably slower rate. At the same time scavenging switch heater 40, now connected through the motor relay winding, is heating the double-throw switch blade 38 of the scavenging switch at a rate which will effect the movement of blade 38 so as to break its cold position with contact 34.

When bimetal blade 38 of the scavenging switch breaks with cold side contact 34, safety switch heater 32' is completely tie-energized and ignition relay winding 16 is de-energized thereby rendering the igniter inoperative. The continued heating and warping of bimetal blade 38 by the scavenging switch heater 44) causes it to close with its hot side contact 36. When this occurs a shunting branch through flame detector contacts 28is established which will effect the bypassing and operative de-energization of motor relay 20 if and when a flame failure results in the reclosing of flame detector contacts 28. This branch extends from the junction of leads 92-94 to the junction of leads 102496 and includes a lead 116, scavenger switch blade 38 in a hot position, the lead 86, the lead 100, flame detector relay contacts 28, and a lead 118. If such flame failure occurs, causing de-energization of motor relay winding 20, its motor contacts 22 will open rendering the burner motor inoperative to supply fuel and its holding contacts 24 will also open, thereby rendering the scavenging switch heater 4t} inoperative. Under such conditions a re-start will occur only after the bimetal blade 38 of the scavenging switch cools and again engages its cold side contact 34. In restarting, pull-in energization of the motor relay winding will be eifected through the described starting-circuit which includes the safety switch 3*!) and its heater 32.

If at any time during normal operation of the burner, a momentary power failure occurs which results in the dropping open of motor relay contacts 24 and 22, a re-start will occur upon resumption of power supply, but only after scavenging switch blade 38 has cooled and again engages its cold side contact 34.

If for any reason the light sensitive element 50 is improperly installed so as to be operatively effected by light other than that of combustion flame, or'if his or becomes defective in a manner to be operatively conductive in the absence of light, the motor relay'winding 2 0 will not be energized upon closing of the thermostat. Thisis so because if the element St) is thus defective the flame detector relay will not be energized upon closing the thermostat to pull in its contacts 28 so as to complete a pull-in circuit for the motor relay winding 20. Under such conditions, however, the ignition relay winding will be energized through the safety switch 30 and its heater 32, and the igniter will operate until the safety switch opens and locks out. i

If upon starting combustiondoes not occur within the predetermined period requiredto open safety switch 30 when safety switch heater 32 is connected through the parallel ignition relay winding 16 and motor relay Winding 2d, the safety switch 30 will open and lock open requiring manual resettin".

By balancing the flame detector relay winding network so that the voltages applied across voltage dependent resistor 44 (when photosensitive element 50 is conductive and when not conductive) lie in that critical range wherein the rate of change of the voltage/current curve is greatest, a substantial amplification of any signal change in the conductance of the photoconductive element is achieved. By rectifying the current flowing through the relay winding 26, a more inexpensive and sensitive flame detection relay may be employed, and by connecting the photoconductive element 59 across this rectified portion of the network so that the current passing through it is alternating, any tendency toward polarization of the semiconductor element 5d is precluded.

in the form of the invention shown in FIG. 1, the igniter is operated upon starting through igniter relay contacts 18 and continues operating untilthe scavenging switch blade 33 parts with its cold side contact 34. This form of operation of the ignition device is referred to as intermittent. If it is desired to maintain operation of the igniter constantly during operation of the burner, the ignition relay winding 16 and its connecting leads 88 and 90 are deleted from the circuit. Also, the ignition relay contacts 18 are deleted and igniter transformer leads 70 and 72 are connected at that point. In this constant ignition arrangement the safety switch heater 32 is in series with the motor relay winding 20 upon starting and the scavenging switch heater 40 is placed in series with the motor relay winding 29 and in parallel with the safety switch heater 3?. when the motor relay winding energizes and its holding contacts 24 close. Also, in this constant ignition arrangement when flame is detected and flame detector relay contacts 28 open, the safety switch heater 32 is completely de-energized by breaking of its circuit at that point instead of being reduced to partial energization by being placed in series with the higher impedance ignition relay coil only as occurs when flame detector contacts open in intermittent ignition operation.

I claim:

1. A flame responsive actuator for a burner control system including a voltage dependent resistor, an actuating relay having a winding, a photoconductive element shielded from a.1 bient light and arranged to see burner flame when it exists, a fixed value resistor, and a power source, circuit connections connecting said fixed resistor, said voltage dependent resistor, and said relay winding in series relationship across said power source, and circuit connections connecting said photoconductive element in parallel with that portion of said circuit connections including said voltage dependent resistor and said relay winding only, said voltage dependent resistor having sufficient conductance at the applied voltage when said parallel connected photoconductive element is nonconductive in the absence of burner flame to permit operative energization of said relay winding, and said photoconductive element being suificiently conductive when burner flame exists to effect a suflicient drop in the applied vo-ltage on said parallel connected voltage dependent resistor to reduce its conductance to the point wherein said relay winding is no longer operatively energized.

2. A flame responsive actuator for a burner control system including a voltage dependent resistor, an actuating relay having a winding, a photoconductive element shielded from ambient light and arranged to see burner flame when it exists, a fixed resistor, a rectifier, a capacitor, and a source of AC. power, circuit connections connecting said fixed resistor, said voltage dependent resistor, said relay winding, and said rectifier in series relationship in that order across said power source, circuit connections connecting said capacitor in parallel with said relay winding only and circuit connections connecting said photoconductive element across that portion of said circuit connections including said voltage dependent resistor, said relay winding, its parallel connected capacitor, and said rectifier only, said voltage dependent resistor having suflicient conductance at the applied voltage when said parallel connected photocond-uctive element is non-conductive in the absence of flame to permit operative energization of said relay winding, and said photoconductive element being sutdcient-ly conductive when burner flame exists to effect a suificient drop in the applied voltage and said parallel connected voltage dependent resistor to reduce its conductance to a point below that which permits operative energization of said relay winding.

3. in a burner control system of the kind described, a limiting resistor, a solid state voltage dependent resistor in which a high rate of change in voltage/current ratio occurs through a predetermined critical range of applied voltages, a control relay having a winding, a solid state .photocouductive element shielded from ambient light and arranged to see a burner flame when it exists, said element having extremely high resistance to the flow of electrical current when the burner flame is non-existent but becoming conductive when flame exists, a source of power, circuit connections connecting said limiting resistor, said voltage dependent resistor, and said control relay winding in series across said power source, and circuit connections connecting said photoconductive element in parallel with that portion of said circuit connections including said voltage dependent resistor and said relay winding only, the resistance value of said limiting resistor and the impedance of said relay winding being such that the voltage across said voltage dependent resistor in the absence of burner flame is near the upper imit of said critical voltage range and is such as to cause a current flow through said voltage dependent resistor which will effect operative energization of said relay winding, and the conductivity of said parallel connected photoconductive element being such when there is burner flame as to increase the voltage drop across said limiting resistor to a point wherein the voltage applied across the voltage dependent resistor is near the lower limit of said critical voltage range and is insuflicient to eflect a flow of current through said voltage dependent resistor which will maintain operative energization of said relay winding.

4. An arrangement as claimed in claim 3 which ineludes means for rectifying the current passing through that portion of the circuit only which is paralleled by said photoconductive element and its circuit connections.

5. An arrangement as claimed in claim 3 which includes a rectifier in series with said voltage dependent resistor and said relay winding, in which a capacitor is connected across said relay winding, and in which said photoconductive element is connected across said voltage dependent resistor, said relay winding, its parallel capacitor, and said rectifier.

6. An arrangement as claimed in claim 5 in which said rectifier is a solid state diode.

7. in an oil burner control system, a main relay having a winding which when energized causes fuel to be supplied to a burner, a starting circuit for energizing said main relay winding including a power source, a space thermostat, said winding, a pair of normally open flame detector relay contacts, a normally closed thermal time switch and a resistance heater for operating said time switch all in series relationship, a parallel running circuit connected across said normally open flame detector relay contacts and said resistance heater andineluding in series relationship normally open main relay holding contacts which close when said main relay winding is energized and a resistor, a flame detector relay including a winding which when energized effects the closing of said flame detector relay contacts to complete said starting circuit, a circuit for said flame detector relay winding including in series relationship said power source,

plied voltage in series with said limiting resistor which,

permits energization of said flame detector relay to effeet the closure of said normally open flame detector relay contacts in said main relay starting circuit, and said voltage dependent resistor having a voltage/current ratio change in the immediate range of the applied voltage which results in a substantial drop in conductivity with a slight drop below the applied voltage, a solid state photoconductive element connected in parallel with that portion of said flame detector relay winding circuit which includes said voltage dependent resistor and said flame detector relay winding, said element being shielded from ambient light and arranged to see flame at the burner, and said element having extremely high resistance in the absence of burner flame, but becoming sufliciently conductive in the presence of burner flame to effect such drop in the applied voltage on the parallel connected voltage dependent resistor as to reduce its conductivity below that which will maintain functional energization of said flame detector relay winding, whereby it said photoconductive element defects for any reason in a manner to become conductive prior to the closing of the space thermostat said starting circuit will not be completed and said main relay winding will not be energized upon closure of said thermostat, and whereby the appearance of burner flame subsequent to the closing of said thermostat in normal operation will effect deenergization of said thermal time switch heater.

8. A control system as set forth in claim 7 in which said flame detector relay winding circuit further includes a solid state diode in series with said relay Winding and said voltage dependent resistor, in which a capacitor is connected across said flame detector relay winding and in which said solid state photoconductive element is connected in parallel with said voltage dependent resister, said winding and said diode, whereby the current passing through said Winding is unidirectional while the current passing through said photoconductive element is alternating.

9. In a burner control circuit, a main relay winding which when energized causes fuel to be supplied to the burner and an ignition relay winding having considerably greater impedance than said main burner relay winding and which when energized effects operation of an ignition device, a source of power, a circuit for said main relay including in series relationship a space thermostat, said power source, a normally closed safety switch, a resistance heater for said safety switch, the cold side contact and common bimetal blade of a doublethrow scavenging switch, normally open flame detector relay contacts, and said main relay winding, circuit connection-s connecting said ignition relay Winding in parallel with that portion of said main relay circuit which includes said normally open flame detector relay contacts and said main relay winding, whereby upon closure of said space thermostat said ignition relay winding is immediately energized, a flame detector relay winding operative when energized to close said flame detector relay contacts to complete a pull-in energizing circuit for said m-ain relay, an energizing circuit for said flame detector relay winding including said power source, said space thermostat, and a light sensitive network including said relay winding and which is sufliciently conductive in the absence of the light of combustion flame to perrnit energization of said winding but which becomes non-conductive in the presence of the light of combustion to eflect its de-energization, a holding circuit for said main relay Winding including a resistance heater of considerably greater resistance than said safety switch heater and which is operative when energized to cause said double-throw scavenging switch blade to move in a predetermined time from its cold side contact to a hot side contact, a pair of normally open main relay contacts which close when said main relay winding energizes, and circuit connections connecting said scavenging switch heater and said main relay contacts in parallel with that portion of said main relay circuit which includes said flame detector relay contacts and said safety switch heater, whereby said safety switch heater is in series with said high impedance ignition relay winding and said scavenging switch heater is in series with said relatively low impedance main relay winding when said flame detector contacts are open, but when said contacts are closed said safety switch heater and said scavenging switch heater are each in series with said parallel connected ignition relay and motor relay windings, thereby permitting relatively rapid heating of the safety'switch when said flame detector contacts are closed in the absence of light and thereby immediately reducing the rate of heating of the safety switch when said flame detector contacts open indicating the presence of light, and a low resistance parallel circuit connected across said motor relay winding and including said flame detector relay contacts and the common blade of said double-throw scavenging switch and its hot side contact, whereby if a change from a condition of light to no light with re spect to said light sensitive network occurs during normal burner operation the main relay winding is shorted through this parallel.

10. A burner control circuit as set forth in claim 9 in which said light sensitive network comprises in series connect-ion a limiting resistor, a solid state voltage dependent resistor in which the voltage/ current ratio changes rapidly in a critical voltage range, the flame detector relay winding, and a solid state diode, a capacitor connected across said relay winding, a solid state photoconductive element shielded from ambient light but arranged to see a burner flame, said element having an extremely high resistance in the absence of burner flame but becoming conductive when flame exists, said element being connected across that portion of the series connection which includes the voltage dependent resistor and the flame detector relay winding the value of said limiting resistor being such that the'voltage applied across said voltage dependent resistor in the absence of burner flame is near the upper limit of said critical voltage range and causes a current flow through said voltage dependent resistor which effects operative energization of the flame detector relay winding, and the conductivity of said parallel connected photoconductive element is such when burner flame exists as to increase the voltage drop across said limiting resistor to a point wherein the voltage applied across said voltage dependent resistor drops to near the lower limit of the critical voltage range and is insuflicient to eflect a current flow through said voltage dependent resistor which will maintain operative energization of said flame detector relay winding.

References Cited in the file of this patent UNITED STATES PATENTS 2,440,700 Rosche May 4, 1948 2,602,847 Larew July 8, 1952 2,924,754 Mead Feb. 9, 1960 2,966,619 7 Burckhardt Dec. 27, 1960 FOREIGN PATENTS 869,876 Great Britain June 7, 1961 

1. A FLAME RESPONSIVE ACTUATOR FOR A BURNER CONTROL SYSTEM INCLUDING A VOLTAGE DEPENDENT RESISTOR, AN ACTUATING RELAY HAVING A WINDING, A PHOTOCONDUCTIVE ELEMENT SHIELDED FROM AMBIENT LIGHT AND ARRANGED TO SEE BURNER FLAME WHEN IT EXISTS, A FIXED VALUE RESISTOR, AND A POWER SOURCE, CIRCUIT CONNECTIONS CONNECTING SAID FIXED RESISTOR, SAID VOLTAGE DEPENDENT RESISTOR, AND SAID RELAY WINDING IN SERIES RELATIONSHIP ACROSS SAID POWER SOURCE, AND CIRCUIT CONNECTIONS CONNECTING SAID PHOTOCONDUCTIVE ELEMENT IN PARALLEL WITH THAT PORTION OF SAID CIRCUIT CONNECTIONS INCLUDING SAID VOLTAGE DEPENDENT RESISTOR AND SAID RELAY WINDING ONLY, SAID VOLTAGE DEPENDENT RESISTOR HAVING SUFFICIENT CONDUCTANCE AT THE APPLIED VOLTAGE WHEN SAID PARALLEL CONNECTED PHOTOCONDUCTIVE ELEMENT IS NONCONDUCTIVE IN THE ABSENCE OF BURNER FLAME TO PERMIT OPERATIVE ENERGIZATION OF SAID RELAY WINDING, AND SAID PHOTOCONDUCTIVE ELEMENT BEING SUFFICIENTLY CONDUCTIVE WHEN BURNER FLAME EXISTS TO EFFECT A SUFFICIENT DROP IN THE APPLIED VOLTAGE ON SAID PARALLEL CONNECTED VOLTAGE DEPENDENT RESISTOR TO REDUCE ITS CONDUCTANCE TO THE POINT WHEREIN SAID RELAY WINDING IS NO LONGER OPERATIVELY ENERGIZED. 